1. Field of the Invention
The present invention relates generally to the testing of semiconductor devices and, more particularly, to the testing of chips within a multi-chip packaged semiconductor device.
2. Related Art
Semiconductor devices have continually evolved to provide improvements such as miniaturization, increased speed, reduced power consumption, and reduced cost. As an example, memory is an essential part of an electronic system because it stores information required by the system, such as computational instructions, preliminary calculation data, temporary data, and various other data. Current semiconductor or integrated circuit (IC) memory devices can store large amounts of data in relatively small packages. Exemplary IC memory devices include random access memory (RAM) devices such as static RAM (SRAM), dynamic RAM (DRAM), non-volatile RAM (NVRAM), and read only memory (ROM) devices such as programmable ROM (PROM), erasable programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), and flash memory.
FIG. 1 illustrates a conventional electronics system 100 comprising a printed circuit (PC) board 102, a system IC 104, and a number of memory devices 106. PC board 102 may be a layered dielectric structure with internal and external wiring that allows system IC 104 and memory devices 106 to be mechanically supported and electrically connected internally to each other and to outside circuits and systems. Memory devices 106 are discrete ICs such as four DRAM ICs of 512 kilobits (Kb) by 32 bits, which may be combined to provide 512 Kb by 128 bits. System IC 104 may comprise, for example, a microprocessor or an application specific integrated circuit (ASIC) that utilizes memory devices 106 to store information. Each of memory devices 106 and system IC 104 may be separately packaged in a suitable package formed of polymer or ceramic and having a plurality of input/output (I/O) pins for connection to PC board 102.
The arrangement of system 100 provides certain advantages, such as ready testing of system IC 104 and memory devices 106 prior to their connection to PC board 102 and easy removal and replacement of faulty discrete components. However, system 100 can be relatively large and may require more space than is available for many types of electronic devices such as cellular telephones, laptops, and personal digital assistants.
FIG. 2 is a block diagram of a conventional multi-chip module (MCM) 200 that integrates a number of raw chips (i.e., the silicon containing the integrated circuit—also referred to as a “die”) into a single semiconductor device. MCM 200 comprises a system chip 202 and a number of memory chips 204 on a substrate 206. System chip 202 and memory chips 204 may correspond functionally to system IC 104 and memory devices 106, respectively, of FIG. 1, but are provided within a single, discrete package. Relative to system 100, MCM 200 provides certain advantages, such as a reduction in the amount of space required for implementation and an increase in processing speeds due to shorter leads between chips.
A multi-chip packaged semiconductor device may be viewed in terms of primary and secondary chips. A primary chip has direct access to external connectors of the multi-chip package and can communicate or convey information directly through these external connectors to components or devices external to the multi-chip package. For example, a primary chip may comprise an application specific integrated circuit (ASIC) controller or microprocessor that performs the main system functions of the multi-chip package. System chip 202 would also be an example of a primary chip.
A secondary chip generally does not have direct access to external connectors and typically is utilized in concert with the primary chip to assist or enhance the primary chip's performance or functionality. For example, a secondary chip may comprise a memory subsystem, co-processor subsystem, analog subsystem, or other application-type specific subsystem. Memory chips 204 would also be an example of secondary chips. Thus, secondary chips generally are not able to “talk” or communicate directly through external connectors.
A drawback of conventional multi-chip packaged semiconductor devices, such as MCM 200, is that it does not allow complete testing of the secondary chips once they are incorporated into the package. For example, in MCM 200, memory chips 204 are connected to system chip 202, with system chip 202 connected to a number of I/O pins 208 of MCM 200. No direct connections are available between memory chips 204 and external test equipment and, thus, a stringent final test of memory chips 204 within MCM 200 is not possible.
Typically, prior to packaging for an MCM, chips are tested using known good die (KGD) technology. There are various levels of KGD technology for die testing. These levels range from wafer level functional and parametric testing (i.e., wafer sort tests) to dynamic burn-in with full testing that continually tests the die while at high temperatures. The more a die is tested, the more likely an assembled MCM will function properly. However, even the most rigorous die testing prior to assembly will not guarantee that the assembled MCM will function as desired. For example, some chips may become damaged during assembly (i.e., after die testing) or the die connections may be faulty within the MCM.
With regard to MCM 200, although is possible to test memory chips 204 by transferring data through other chips (e.g., system chip 202), this type of testing fails to detect all of the various types of memory failures. Specifically, external integrated circuit test equipment does not have direct access to the secondary chips because there are no pin-outs or other direct connections, because secondary chips interface through the primary chips. Consequently, a number of MCM failures are the result of integrated circuit chips that have not been fully tested. Often, these failures are not discovered until after incorporation into an electronic device, which adds to the cumulative cost of the defective MCM, not only for the MCM manufacturer, but also for their customers whose products fail to function properly due to the defective MCM. Thus, for complete testing and for quality and reliability reasons, direct access to secondary chips is required.
As a result, there is a clear need for a system and method to test one or more chips of a multi-chip semiconductor package after integration into the chip packaging (e.g., MCM packaging).